It's more a question of things like if you're building the Swift compiler in your CI system with macOS nodes less than 10.15, then you'll have to upgrade them.

It's more a question of things like if you're building the Swift compiler in your CI system with macOS nodes less than 10.15, then you'll have to upgrade them. That can be problems if the build nodes you're building on are on hardware that doesn't support macOS 10.15. Now you have to buy a whole new Mac Mini or whatever just to continue building.